The invention relates to a surgical material based on liquid monomeric and powdered polymeric acrylates and/or methacrylates that changes into solid state by way of a plastic state due to the addition of catalysts, accelerators, and, optionally, conventional additives once the liquid and powdered constituents have been mixed together. The resulting pastes are especially appropriate for use as "bone cements" in the implantation of artificial hip and knee joints, and the like, in bone.
Bone cements based on methyl methacrylate and polymethyl methacrylate have been employed in bone surgery for many years. They consist of a liquid constituent and of a solid constituent that are stored separately and mixed together for use. The mixture is pasty or creamy and is employed in that state, curing subsequent to application in the body. The solid constituent usually consists of powdered polymethyl methacrylate, a polymerization initiator, and optionally an X-ray contrast agent such as barium sulphate or zirconium dioxide. The powder can also include such antibiotics as gentamicin, such short reinforcing fibers as carbon fibers, and such bone-growth promoters as calcium phosphate. The liquid constituent consists of monomeric methyl methacrylate, an accelerator, and optionally a dye. The two constituents are mixed in a ratio of approximately 2:1 just before processing, are ready to use in approximately 4 to 6 minutes, and cure in 6 to 15 minutes.
The advantages of bone cements of this type are their good compatibility with the tissue, their rapid curing rate, and the powerful strength of the hardened cement. In contrast to these advantages, however, are such drawbacks as the comparatively high temperatures that occur during polymerization and can lead to damage to the surrounding tissue and hence to loosening of the bond.
Another drawback of the methyl-methacrylate based cements employed in joint operations up to now is their release of residual monomers. Monomeric methyl methacrylate gets into the bloodstream and can lead to fatty embolisms that entail cardiocirculatory complications severe enough to cause cardiac arrest.
These drawbacks are eliminated by a bone cement described in German patent No. 2 552 070, which contains a liquid constituent in the form of an emulsion of methyl methacrylate, water, an emulsifier, and an accelerator. Bone cements prepared in accordance with this method have a lower maximal curing temperature and a lower content of residual monomer, and wet the irregularities in the surface of the bone better.
In addition to these advantages, however, emulsion-type cements have drawbacks, especially in relation to convenience. The emulsions have viscosities of 200 to 800 MPa.multidot.sec and have to be vigorously shaken before they can be poured out of the ampoule. Shaking, however, is inconvenient and time-consuming while an operation is going on, and extreme care must be taken to ensure that the ampoule is completely emptied and to prevent spattering when the emulsion is knocked out. Furthermore, aqueous emulsions are sensitive to freezing when stored.
German patent application No. 3 245 956.4 describes a bone cement with a liquid constituent that contains aliphatic esters of saturated mono-, di-, or tri-carboxylic acids with 1 to 6 carbon atoms and optionally either 1 or 2 hydroxy groups partly or completely esterified with 1-, 2-, or 3-valence alcohols with 1 to 4 carbon atoms, or liquid esters, specifically polyethylene glycol or 1,2- or 1,3-polypropylene glycol, each with 2 to 30 glycol units.
It has, however, become evident that, although the aforesaid liquids do have the advantages described in the application and are not toxic in general, they possess a certain cytotoxicity.